The mark of Cain plays an important role in Sinclair's development. Demian's alternate explanation of this mark as one of distinction, rather than shame, is the first serious intellectual challenge ever presented to Sinclair's Christian beliefs. As an adolescent, Sinclair often recalls this interpretation and the conversation in which it was offered, deriving great comfort from it. This motif extends beyond the biblical mark of Cain, however. Demian often tells Sinclair that he bears a certain mark, though it is more or less visible at different times. Similarly, Frau Eva recognizes Sinclair immediately upon meeting him, presumably because of this mark. This mark is intended to distinguish Sinclair as special, just as Demian interprets Cain's mark to indicate his superiority. This motif illuminates Sinclair's character—it sets him up as different and shows that this difference carries very different moral values for different people. Just as a schoolteacher and Demian differ in their interpretation of Cain's mark, so to do mainstream society and Demian differ in their opinions of Sinclair's difference.
The notion of a mentor-mentee relationship is central to Demian. Sinclair does not set out on the road to self-discovery alone. Rather, he is brought there by Demian and led through it by both Demian, Pistorius, and, in the end, Eva. For Hesse, unlike for many others, self-discovery does not mean sitting in a room alone and contemplating. Rather, it can be an interactive activity wherein one person helps another. In fact, these mentoring relationships are valuable to Sinclair not only because they lead him to change his world-view, but also for the friendship and kinship they provide. Some of the strongest emotions Sinclair ever feels are for his mentors—Demian and especially Eva.